Question: A box contains $11$ red marbles, $7$ green marbles, and $11$ blue marbles. If a marble is randomly chosen, what is the probability that it is not blue?
Explanation: There are $11 + 7 + 11 = 29$ marbles in the box. There are $11$ blue marbles. That means $29 - 11 = 18$ are not blue. The probability is $ \frac{18}{29}$.